The invention relates to a filter apparatus for the filtering of substances from a fluid.
There is a need in many industrial processes to subject a fluid to filtering prior to its further use in order to remove unwanted contaminants from the fluid. The manufacture of semi-conductors and chips can be named as an example here. For example, the photoresists applied to the semi-conductor structures must satisfy the highest demands on cleanliness. Process filters are also necessary in the chemical-mechanical polishing (CMP) processes in which a suspension known as a slurry, typically made up of very fine solid particles and of a liquid, is applied to a rotating wafer and serves there for the polishing or lapping of the very fine semi-conductor structures, in order to remove any contaminants or clumps which may be present from the slurry. Such contaminants could cause substantial damage on the sensitive semi-conductor structures.
Such processes are frequently carried out in clean rooms of the highest category (class 1). Since these clean rooms are very cost-intensive, it is desirable to have apparatuses available which are as small and compact as possible and which have low space requirements.
Since the fluids used in semi-conductor production are frequently highly abrasive (e.g. slurry) or are chemically very aggressive, special materials are used for the process filters. The filter element or the filter membrane is frequently made of polytetrafluorethylene (PTFE, commercial name Teflon).
The perfluoroalkoxy copolymer (PFA) is frequently used for the manufacture of the filter housing and is characterized by its high chemical resistance with respect to aggressive substances and has the advantage in comparison with PTFE that it can be processed by means of injection molding processes.
In addition to filtering, it is also frequently a necessity in the processes to heat the fluid to a predetermined temperature or to regulate the temperature of the fluid in order to ensure optimum process management. It is, for example, known for this purpose to bring the PFA housings which contain the fluid or through which the fluid flows into thermal contact with a heat carrier according to the principle of a heat exchanger. Since, however, PFA is a poor heat conductor, such heating systems come with the disadvantage of a high thermal time constant. This thermal inertia makes a regulation of the temperature at least very difficult.
It is furthermore known to use infrared radiation for the heating of the fluids. However, for this purpose, an optical access to the fluid is necessary. It is, for example, possible to arrange a plurality of glass tubes around an infrared source and to allow the fluid to flow through these glass tubes in which the fluid can then be acted on by infrared radiation. This method can, however, not be used for very corrosive liquids such as hydrofluoric acid (HF) because such liquids attack the glass.